Papers by Keyword: Age Hardening

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Authors: Bradley Diak, Rathna Lanerolle
Abstract: The age hardening response of a quasi-binary Al-Mg2Si alloy was studied using activation distance analysis of precise strain rate sensitivity experiments at 78 and 300K. The alloy of Al-0.7Mg-0.33Si-0.024Fe-0.006Ti(at.%) has a stochiometrically balanced composition of Mg2Si. The alloy was solutionized at 550°C and ice water quenched before ageing in one of two ways: single-step or multi-step ageing. For single-step ageing: specimens were naturally aged for 70 days at room temperature (RT); pre-aged for 16 hours at 70°C; or artificially aged for 30 min or 10 hours at 175°C. For multi-step ageing: specimens were pre-aged at 70°C for 16 hours after natural ageing for 70 days at RT; artificially aged for 30 min or 10 hours at 175°C after pre-aging at 70°C for 16 hours; or artificially aged for 10 hours at 175°C after natural aging for 70 days at RT. The activation analysis reveals rate controlling obstacle dimensions ranging from 0.3 to 10 nm depending upon the ageing condition. A comparison is made to a prior three dimensional atom probe ageing study of the same alloy [Murayama and Hono, Acta Mater., 47 (1999) 1537-1578.].
Authors: Simon P. Ringer
Abstract: This paper sets out the needs for and recent advances in microscopy in Al alloys, using solutesolute and solute-vacancy clustering as examples. Cluster-assisted nucleation and cluster strengthening are discussed and this is followed by a discussion of the local electrode atom probe. Heuristic and algorithmic tools for assessing the nanoscale microstructure or nanostructure of Al alloys acquired from atom probe tomography experiments are then presented.
Authors: Seiji Saikawa, Chiharu Otsubo, Susumu Ikeno, Koichi Komai
Abstract: Al-Li alloys have higher mechanical properties and more lightweight than other conventional aluminum alloys. Therefore , it is focused as a good material for weight reduction of industrial fields. However, since the Al-Li alloy are highly active and hard to cast, there has been limited research on casting. In this study, age-hardening behavior of Al-2.5mass%Li alloys cast into sand and metal mold were investigated. All alloys cast into Y-block shape sand mold, and then artificial aged after solution treated at 743K for 36ks. Because of difference in quantity of precipitation by metastable δ’(Al3Li) phase, peak hardness of metal mold casting is higher than that of sand molds castings.
Authors: Nouari Saheb, Abdullah Khalil, Abbas Saeed Hakeem, Tahar Laoui, N. Al-Aqeeli, A.M. Al-Qutub
Abstract: In the present work, age hardening behavior of CNT reinforced Al6061 and Al2124 nanocomposites, prepared by ball milling and spark plasma sintering, was investigated. The effect of CNT content, annealing time and temperature on the age hardening behavior of the nanocomposites was evaluated and compared to the monolithic alloys prepared and age hardened under the same conditions. It was found that CNTs have a negative influence on the age hardening of the alloys. The alloys displayed standard age hardening behavior i.e. a sharp increase in hardness during initial aging followed by a steady decrease in hardness. Whereas the nanocomposites did not only display initial softening during aging but also showed reduced age hardening efficiency. The hardening efficiency was found to decrease with increasing CNT content. The complicated behavior of nanocomposites was explained in terms of dislocation recovery, large thermal mismatch between matrix and CNTs and bulk microstructure of the composites.
Authors: A. Rose, O. Kessler, Fabian Hoffmann, H.W. Zoch, P. Krug
Abstract: For quenching of age hardenable aluminum alloys today predominantly aqueous quenching media are used, which can lead due to the Leidenfrost phenomenon to a non-uniform cooling of the parts and thus to distortion. In relation to the conventional quenching procedures in aqueous media, gas quenching exhibits a number of technological, ecological, and economical advantages. The quenching intensity can be adjusted by the variable parameters gas pressure, gas velocity as well as the kind of gas and thus can be adapted to the requirements of the component. By the higher uniformity and the better reproducibility, gas quenching offers a high potential to reduce distortion. Cost savings would be possible, because of reduced distortion and therefore less reworking. High-pressure gas quenching with nitrogen or helium, as well as air quenching at ambient pressure in a gas nozzle field was applied to the spray formed aluminum alloy Al-17Si-4Fe-3Cu-0.5Mg-0.4Zr (DISPAL S232). Hardness and tensile tests have been carried out to determine the mechanical properties after gas quenching and aging compared to water quenching. The distortion behavior of a forged aluminum component of the spray formed alloy was examined after gas quenching and after water quenching. Gas quenching showed remarkable advantages regarding distortion.
Authors: Abu Syed Humaun Kabir, Jing Su, Mehdi Sanjari, In Ho Jung, Stephen Yue
Abstract: Precipitation hardening has been used before as one of the most effective strengthening methods for many metallic alloys. However, this method has not been studied completely in magnesium alloys, and the numbers of precipitation hardenable wrought Mg alloys are still very limited compared to aluminum alloys and steels. The age hardening responses of Mg-Al-Sn alloys in cast-homogenized condition were investigated by isothermal aging at 200°C for prolonged time. It was found that hardness can be improved significantly for the alloy with higher amounts of tin. The improvement in hardness was reasoned by the formation of precipitates. The shapes and morphology of the precipitates were different depending on the orientations of the grains. The precipitates were characterized by scanning electron microscope.
Authors: Prasanta Kumar Rout, K.S. Ghosh
Abstract: Artificial aging behaviour of a 7017 Al-Zn-Mg alloy was studied by hardness measurement. The electrochemical behaviour of various alloy tempers, such as under-, peak-, and over-aged, have been evaluated by measuring variation of open circuit potential (OCP) with time and potentiodynamic polarization study in different environments. All the alloy tempers were tested in 3.5 wt. % NaCl solution at neutral (pH 7), at acidic (pH 1) and at alkaline (pH 12) conditions. It has been observed that the OCP values of the alloy tempers shifted toward noble direction with the increase of aging time in 3.5 wt. % NaCl solution. The polarization curves are more or less similar in shape exhibiting only active region in neutral (pH 7) and in acidic (pH 1) conditions, but an active-passive region at alkaline (pH 12) condition. The electrochemical parameters; Ecorr, Icorr, passive potential range (Ep) and passive current (ip), obtained from potentiodyanamic polarization curves for the alloy tempers in acid, neutral and alkaline solution; depend on the alloy tempers and the pH of the solution as well. Attempts have been made to explain the observed electrochemical behaviour of the alloy tempers, which is influenced by the microstructure, presence and distribution of second phase precipitates, accessed by DSC and XRD techniques.
Authors: Seung Won Lee, Daichi Akama, Z. Horita, Tetsuya Masuda, Shoichi Hirosawa, Kenji Matsuda
Abstract: This study presents an application of high-pressure torsion (HPT) to an Al-Li-Cu-Mg alloy (2091). The alloy was subjected to solid solution treatment at 505oC for 30 minutes and was processed by HPT under 6 GPa for 5 revolutions at room temperature. The hardness increased with straining and saturated to a constant level at 225 Hv. Aging was undertaken on the HPT-processed alloy at 100, 150 and 190oC for the total periods up to 9.3 days. The aging treatment led to a further increase in the hardness to ~275 Hv. It is shown that the simultaneous strengthening of the alloy due to grain refinement and age hardening was successfully achieved by application of HPT and subsequent aging treatment. The enhancement of the strength is prominent when compared with the application of a conventional rolling process.
Authors: Dong Geun Lee, Cheng Lin Li, Jung Wha Seo, Xu Jun Mi, Yong Tae Lee
Abstract: Ageing behaviors and microstructural characterization by aging condition of Ti-Al-Mo-Fe alloy was investigated. Due to the formation of ω phase, it occurs a drastic change in mechanical properties of β alloys. There is large increasing in hardness and yield strength, accompanied with serious ductility reduction. However, it has been proved that proper control of ω phase volume fraction can bring to improve strength with a reasonable ductility. In this work new beta titanium alloy was designed and developed in Ti-Al-Mo-Fe alloy to investigate the hardening behavior of ω and α precipitation during aging. The results showed that a small amount of athermal ω was observed in the β matrix during water quenching from above the β transus temperature. Isothermal ω formation was also found during aged at temperatures ranging from 573 K to 773 K although it has a limited time of stability at 773 K. The hardening due to isothermal ω precipitation exhibits no over-aging effect as long as ω phase exists inside the matrix. The hardness of this alloy is very sensitive to size and volume fraction of ω phase and its existence, which depends on aging temperature, time and alloy compositions.
Authors: Makoto Ando, Yoshikazu Suzuki, Akio Niikura, Goroh Itoh
Abstract: Creep behavior of an Al-0.3%Mg-0.5%Si alloy affected by pre-aging condition was investigated to obtain fundamental knowledge on the thermal stability in the service temperature range for the precipitation-hardened aluminum heat-exchanger. The alloy was aged at 175 °C for 3 h (under-aged) and 24 h (peak-aged), after solution treatment, and then subjected to creep testing at temperatures of 150 °C and 200 °C. When the creep temperature was 150 °C, the under-aged (UA) specimen showed a lower creep rate than that of the peak-aged (PA) specimen. On the other hand, when the creep temperature was 200°C, both specimens showed almost the same creep rate. In other words, the UA specimen had higher creep resistance than the PA specimen at 150 °C, whereas this advantage disappeared at 200 °C. The difference was thought to originate from the precipitation during creep testing.
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